The staphylococcal epidermolytic toxin syndrome (SETS) was suspected to be different from severe erythema multiforme or toxic epidermal necrolysis. This was based on localized staphylococcal infections, phage typing of staphylococci and histologic findings. Strong evidence for the delineation of SETS as a distinct entity came from establishment of a murine model of epidermolysis. This occurred after intraperitoneal injection with live staphylococcal or broth filtrates from selected strains. Purification of the responsible staphylococcal proteins was accomplished in several laboratories in the early 1970's. Although many epidemics of pemphigus neonatorum and SETS were attribiuted to beta lactamase-producing, phage group II staphylococci, other staphylococcal exoproteins became implicated. A phage group I strain was shown to produce the appropriate toxin without an associated plasmid. We now utilize our prior experience in the protein chemistry of epidermolytic toxins of chromosomal or plasmid origin, antisera to these proteins and our isolate of the gene (extC) contained in a 13.3 kilobase fragment cloned from S. aureus strain EV. We have established that E. coli transfected with pTW103 produces epidermolytic toxin A in a functionally active form. The experiments proposed will allow us to: (1) complete the restriction endonuclease mapping of plasmid TW103 and plasmid ETc01, (2) determine the sequence of the structural gene for epidermolytic toxin A and analysis of flanking sequences contained in the plasmid ETc01 gene fragment, (3) construct a probe for rapid diagnosis of staphylococcal strains containing the gene for extC and to search for homologous ext genes, (4) generation of a series of mutants to ascertain critical structural portions of the epidermolytic toxin gene. Structural information will be compared with published N-terminal sequences for ETc and ETp. Determination of the sites related to this epitope reacting in immunoassays should be forth-coming. Utilization of the data may prove worthwhile should vaccine development be considered in this disease, which can have up to 10% mortality.